Is it possible to run mplayer w/ VDPAU on multiple monitors? For example, play 1920x1080 video at full resolution via HDMI and play the same video at the same time letterboxed and scaled on 1280x1024 monitor via VGA? I have found options for specifying which monitor but no example for outputting to two displays at once.

However, you would need to implement this one of two ways, neither of which is implemented in MPlayer:

a) Create output surfaces the size of the entire desktop, and have MPlayer use VDPAU's rendering operations to render the video twice, based on the portions of the desktop that the displays scan out (Xinerama information would be useful to determine this, I think).

b) Create two separate windows, one per display device (assuming zero overlap), and a separate presentation queue for each window, and then display each frame via each presentation queue at the same time. MPlayer would probably need to use timestamps for presentation to ensure that the displays did not drift apart, which it doesn't currently do in SVN versions.